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A pregnant Southern platyfish. Pregnancy has been traditionally defined as the period of time eggs are incubated in the body after the egg-sperm union. [1] Although the term often refers to placental mammals, it has also been used in the titles of many international, peer-reviewed, scientific articles on fish.
The traditional modes of reproduction include oviparity, taken to be the ancestral condition, traditionally where either unfertilised oocytes or fertilised eggs are spawned, and viviparity traditionally including any mechanism where young are born live, or where the development of the young is supported by either parent in or on any part of their body.
Most male fish have two testes of similar size. In the case of sharks, the testes on the right side is usually larger [citation needed].The primitive jawless fish have only a single testis, located in the midline of the body, although even this forms from the fusion of paired structures in the embryo.
Current research suggests that 2-3 servings of low-methylmercury containing fish per week in pregnancy is both safe and beneficial. [6] Mercury accumulates in fish through their own diet (bioaccumulation). A general rule of thumb is that fish higher up on the food chain, and with longer life spans will contain higher levels of mercury.
External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. [1] It is contrasted with internal fertilization, in which sperm are introduced via insemination and then combine with an egg inside the body of a female organism.
Pregnant male pipefish can absorb nutrients from their broods, in a manner very similar to filial cannibalism found in many other families of fish. The smallest eggs in a brood of various egg sizes usually have lower survival rates than larger ones due to the larger eggs having a longer-lasting food source (absent contributions from the father ...
Superfetation (also spelled superfoetation – see fetus) is the simultaneous occurrence of more than one stage of developing offspring in the same animal. [1] [2] [3]In mammals, it manifests as the formation of an embryo from a subsequent menstrual cycle, while another embryo or fetus is already present in the uterus.
Pregnancy usually occurs by sexual intercourse, but can also occur through assisted reproductive technology procedures. [6] A pregnancy may end in a live birth, a miscarriage, an induced abortion, or a stillbirth. Childbirth typically occurs around 40 weeks from the start of the last menstrual period (LMP), a span known as the gestational age.